The present invention relates generally to the art of electrical circuit interrupting devices. More particularly, the invention relates to a device for physically disconnecting a current path between two electrical conductors in response to an overcurrent condition or a circuit malfunction, such as a short circuit.
A large number of devices are known for interrupting electrical power between conductors in response to overcurrent conditions, such as short circuits, phase loss, ground faults and the like. Such devices are typically designed into both residential and industrial electrical systems for protecting electrical wiring, as well as devices such as appliances and electric motors. In general, such protective devices include fuses and circuit breakers. Fuses are typically sacrificed by the overcurrent condition and are thereafter replaced. Circuit breakers, on the other hand, typically physically open contacts in response to a tripping event, and may thereafter be reset, either automatically following a cooling period, or by physical intervention of a user.
While existing circuit interrupting devices of this type offer a range of response times and protection characteristics, they are not without drawbacks. For example, in certain environments and applications where extremely rapid power interruption is required, semiconductor fuses generally offer satisfactory response time, on the order of 0.6 milliseconds. However, such fuses are relatively expensive and must be physically replaced following a tripping event. While circuit breakers of known design may be reset, thereby avoiding the additional cost of replacement after a tripping event, they are typically substantially slower than fuses, having turnoff times (i.e. time to open and interrupt power) of typically 4 milliseconds. Moreover, the let-through energy in such devices increases as a function of the cube of their turnoff time, so long as the current rise is controlled by the source voltage and the circuit inductance, which is typically the case for a hard fault. Thus, circuit breakers responding in twice the time as fuses let through some eight times the energy, increasing the risk of damage to wiring or electrical devices intended to be protected.
There is a need, therefore for an improved circuit interrupting device that is capable of responding extremely rapidly to overcurrent conditions to interrupt power between conductors. Furthermore, there is a need for an improved circuit interrupting device having a turnoff response time comparable to semiconductor fuses, but that is not sacrificed by the overcurrent condition. Furthermore, there is a need for a rapid circuit interrupter of relatively simple construction capable of being incorporated into a circuit breaker and reset following a tripping event, in a manner similar to a conventional circuit breaker.